Method and device for controlling a synchronous motor with permanent magnet

Abstract

A method and device for controlling a synchronous permanent magnet motor with at least one phase, a coil and a rotor, wherein the method and device controls the powering of each motor phase, simultaneously measures the voltage of each motor phase, determines the rotor speed and the motor load from the measured voltage; determines a variable frequency from the speed and the load, samples at the variable frequency output signals from the voltage measurement of each phase; determines the rotor position from the sampled signals; and controls the powering of each motor phase as a function of the rotor position. The device is powered from an electric power source and comprises a power bridge powering the motor coil, a unit for controlling the powering of the coil, a circuit for measuring the voltage of each motor phase and means for sampling, at a variable frequency, signals from the measuring circuit.

What is claimed is:  
     
       1. A method for controlling a synchronous permanent magnet motor with at least one phase, a coil and a rotor, comprising the steps of: 
       controlling the powering of each motor phase;  
       simultaneously measuring the voltage of each motor phase;  
       determining a rotor speed and a motor load from said measured voltage;  
       determining a variable frequency from said speed and said load;  
       sampling at said variable frequency output signals from the voltage measurement of each phase;  
       determining the rotor position from the sampled signals; and  
       controlling the powering of each motor phase as a function of the rotor position.  
     
     
       2. Method according to claim  1 , wherein said coil is powered in a unidirectional manner. 
     
     
       3. Method according to claim  1 , wherein said coil is powered in a bi-directional manner. 
     
     
       4. Method according to claim  1 , wherein the rotor rotational speed is determined by introducing the voltage of at least one motor phase into a comparator ( 33 ,  34 ,  35 ) and by measuring the time interval which separates two sign changes in the signals from said comparator. 
     
     
       5. Method according to claim  1 , wherein the rotor rotational speed is determined by calculating the sum of the squares of the voltages of each phase and by extracting the square root of this sum. 
     
     
       6. Method according to claim  1 , wherein the powering of the motor is switched as a function of the number of motor phases, the phase powering type, the motor type and the operating mode thereof. 
     
     
       7. Method according to claim  6 , wherein as a function of the rotor position, only one type of switching is authorized. 
     
     
       8. Method according to claim  1 , wherein, when the time separating two successive actions for controlling the powering of each motor phase exceeds a predefined threshold value, the variable sampling frequency is fixed at a predetermined value greater than the maximum rotational speed of the rotor. 
     
     
       9. Method according to claim  1 , further comprising the steps of: 
       repeatedly determining the real rotational speed of the rotor;  
       comparing this real rotational speed to a predefined threshold value;  
       controlling the powering of each motor phase by momentarily cutting it off when the real speed is less than the threshold speed;  
       controlling the powering of each motor phase by measuring the voltage induced by the rotor movement over a non-powered phase, when the real speed is greater than the threshold speed.  
     
     
       10. Device for controlling a synchronous permanent magnet motor with at least one phase, a coil and a rotor, wherein the device controls: (a) the powering of each motor phase, (b) simultaneously measures the voltage of each motor phase, (c) determines the rotor speed and the motor load from said measured voltage; (d) determines a variable frequency from said speed and said load, (e) samples at said variable frequency output signals from the voltage measurement of each phase; (f) determines the rotor position from the sampled signals; and (g) controls the powering of each motor phase as a function of the rotor position, wherein said device is powered by an electric power source, wherein said device comprises: a power bridge ( 13 ) powering the motor coil, a unit for controlling the powering of the coil, a circuit for measuring the voltage of each motor phase and means for sampling, at a variable frequency, signals from said measuring circuit. 
     
     
       11. Device according to claim  10 , further comprising a control unit arranged to control the switching of the powering of each motor phase, and wherein this control unit includes at least one control program depending on the motor type, the number of phases, the phase powering type and the motor operating mode. 
     
     
       12. Device according to claim  10 , further comprising a phase comparator arranged for measuring the sign of each phase. 
     
     
       13. Device according to claim  10 , wherein the voltage of each phase is introduced into the control unit in the form of analogue signals.